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Keywords:

  • air–sea interaction;
  • diurnal cycle;
  • intraseasonal variability;
  • mixed layer;
  • monthly forecasting

Abstract

The role of coupled processes in the Madden–Julian Oscillation (MJO) is investigated in the European Centre for Medium-Range Weather Forecasts Monthly Forecasting System.

A series of forecasts initialized daily for 47 days during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) period are performed with sea surface temperatures (SSTs) provided by persistence of initial conditions, and coupling to either a full dynamical ocean model with vertical resolution in the upper ocean typical of coupled models (10 m), or, a 1D mixed layer ocean model with high (∼1 m) vertical resolution in the upper ocean.

The experiment with the full dynamical model shows improved skill compared with the persisted SST experiment, indicating a role for coupled processes in the MJO. The experiment with the mixed layer model shows a further improvement in skill over the full dynamical ocean, particularly for the phases of the MJO where the convection is active over the Indian Ocean or West Pacific. This further improvement comes about from an enhanced sensitivity of the SST to the surface flux anomalies associated with the MJO.

Additional sensitivity experiments reveal that the improved representation of the diurnal cycle which results from the increased vertical resolution is a significant factor in the improved skill of the experiments with the mixed layer model. Copyright © 2007 Royal Meteorological Society